Influence mechanism of machining parameters on surface quality and subsurface damage of single crystal γ-TiAl

To study the influence mechanism of machining process parameters on surface quality and subsurface damage of nano-cutting single crystal γ-TiAl alloy, molecular dynamics(MD) was used as the basic theory. Using a non-rigid diamond tool, a three-dimensional nano-cutting model was established, and the influence of different cutting speeds and depths of cut on the surface and subsurface structure were analyzed in detail by studying chip volume, surface roughness, workpiece hydrostatic pressure distribution, dislocation density, dislocation evolution, and phase transitions atomic number. The results showed that with the increase of cutting speed, the chip volume increases, the machining efficiency improves and there is a critical value of the cutting speed of 100 m/s, the surface roughness first decreases and then increases and there is also a critical value of the cutting speed of 100 m/s, the complexity of dislocations reduces, the density of dislocations decreases, and the degree of plastic deformation increases. However, with the increase of cutting depth, the chip volume increases, the machining efficiency improves, the surface roughness, the density of dislocations and the degree of plastic deformation increase significantly, and it was found that the dislocations were mainly distributed in front of and below the tool during cutting process, and there were V-shaped dislocations and stair rod dislocations in the direction of 45o in front of the tool, as well as dislocations reacting with each other, and stable defects such as vacancies and atomic clusters remained after the cutting process

Hot stretch forming of titanium sheet by resistance heating

Titanium alloys are important aerospace materials due to excellent comprehensive performance, but it is difficult to form at room temperature. Electrically assisted hot stretch forming is used to form the titanium panels of aircraft. This paper studies the effect of temperature, strain, stress relaxation time and cooling rate on forming accuracy by stress relaxation test, tensile test and forming experiment. It is shown that for the influence of temperature on forming accuracy, there is no large difference among 773K, 873K, 973K. And with increase of strain, the forming accuracy becomes lower. For the influence of stress relaxation time, there is no large difference among 0min, 15mins, 30mins. And with decrease of cooling rate, the forming accuracy is improved significantly. It’s concluded that when the temperature reaches a high level, temperature and stress relaxation time have no great influence on forming accuracy. And the forming accuracy is mainly influenced by strain and cooling rate. Electrically assisted hot stretch forming is an effective method to form titanium alloy. And the part with high forming accuracy can be obtained by adopting high temperature, low strain, proper stress relaxation time and low cooling rate

Three new species of Candolleomyces (Agaricomycetes, Agaricales, Psathyrellaceae) from the Yanshan Mountains in China

Three new species, Candolleomyces incanus, C. subcandolleanus and C. yanshanensis, were found and described from Yanshan Mountains in China. The identification is based on morphological observation combined with phylogenetic analysis of ITS-LSU-Tef1α-TUB2. This study enriched the species diversity of Candolleomyces in Yanshan Mountains and provided important data support for the systematic study of Candolleomyces in the future

Enhanced Precision Through Multiple Reads for LDPC Decoding in Flash Memories

Abstract—Multiple reads of the same Flash memory cell with distinct word-line voltages provide enhanced precision for LDPC decoding. In this paper, the word-line voltages are optimized by maximizing the mutual information (MI) of the quantized channel. The enhanced precision from a few additional reads allows FER performance to approach that of full precision soft information and enables an LDPC code to significantly outperform a BCH code. A constant-ratio constraint provides a significant simplification in the optimization with no noticeable loss in performance. For a well-designed LDPC code, the quantization that maximizes the mutual information also minimizes the frame error rate in our simulations. However, for an example LDPC code with a high error floor caused by small absorbing sets, the MMI quantization does not provide the lowest frame error rate. The best quantization in this case introduces more erasures than would be optimal for the channel MI in order to mitigate the absorbing sets of the poorly designed code. The paper also identifies a trade-off in LDPC code design when decoding is performed with multiple precision levels; the best code at one level of precision will typically not be the best code at a different level of precision

Exergy analysis of a high concentration photovoltaic and thermal system for comprehensive use of heat and electricity

By analyzing the temperature distribution cloud image of the solar cell, it was found that the temperature distribution was uneven and there was a large temperature gradient, resulting in reduced effective cell size requiring a dual inlet model. At the same time, simulations and experiments were established, and it was found that the simulation results were consistent with the experimental results. This paper offers the first law of thermodynamics efficiency and exergy analysis of a simple optimized model at different inlet flow, concentration ratios and inlet temperatures. The result shows that while the inlet flow is 0.02–0.06 kg/s, the system runs efficiently, which can provide considerable heat output, and has greater protection for the cell. When the concentration ratio increases, thermodynamic efficiency and exergy efficiency will decrease, but the total output exergy is in an increasing trend and the trend will decrease as the concentration ratio increases. As the temperature of cooling water increases, the thermal and overall exergetic efficiencies will also increase, and when the inlet temperature is 60 °C, the electrical efficiency is still greater than 20%. In practical applications, the quality of thermal energy can be improved by increasing cooling water temperature, broadening the field of application